TL;DR
Landing pad unloading bays are currently hard-coded to only allow unloading when connected to a cargo landing pad, it would be cool if they worked with space platform hubs, too.WHAT?
When removing the surface condition restriction for landing pad unloading bays, they can be placed on space platforms. However there, they only function as cargo bays (minus input/output rocket capability) even though by the in-game logic the very same cargo bay mechanisms are at play for both landing pads and space platform hubs.This is purely a modding thing. In the vanilla game, the restriction on landing pad unloading bays that they need gravity is sufficient to prevent their use in orbit.